phenomenal vs unheard-of

phenomenal

adj
  • Very remarkable; highly extraordinary; amazing. 

  • Of or pertaining to the appearance of the world, as opposed to the ultimate nature of the world as it is in itself. 

  • Perceptible by the senses through immediate experience. 

unheard-of

adj
  • Previously unknown; unprecedented. 

  • Unknown or known to only few people. 

How often have the words phenomenal and unheard-of occurred in a corpus of books? (source: Google Ngram Viewer )